The invention relates to a device for applying plant protecting compositions and the like.
A device of this kind is known from EP-A-201 981 in which, in order to keep the concentration of the active substance in the carrier fluid constant irrespective of the driving speed of the tractor to which the device is attached, the volume of carrier fluid supplied by the feed pump to the spray nozzles is controlled, as a function of the amount of active substance added, by an electric control means that monitors one of the two fluid flows. Although the amount of active substance is controlled as a function of the driving speed, the concentration remains independent of the driving speed. The metering pump for the active substance is driven by a motor. It is said, however, also to be possible for the metering pump to be so designed that it is driven by the pressurised carrier fluid supplied by the feed pump. How, in that case, the metering pump is designed, and how the volume of carrier fluid is supposed to be controlled as a function of the amount of active substance added, is not specified. In that device, keeping the concentration of active substance in the carrier fluid constant irrespective of the driving speed necessitates a complicated control means that matches the drive of the feed pump to the amount of active substance supplied. To adjust the concentration of the active substance in the carrier fluid, the drive of the metering pump is modified by the control means, thus requiring the control means to have a further function.
AU-B-504 816 discloses a device for metering a liquid fertilizer or the like into a stream of water flowing through a main pipe, a reduction in pressure in the water flow being produced by a reduction in cross-section, for example a Venturi nozzle, in the main pipe. Pipelines are connected to the main pipe, one upstream and one downstream from this reduction in cross-section, each of which leads to a pump that is connected by way of an immersed pipe to a container housing the preparation. As a result of the higher pressure in the pipeline connected upstream from the reduction in cross-section, a diaphragm piston in the pump is acted upon, this piston, which is provided with valves and biassed by a spring, sucking fertilizer out of the container, and the fertilizer being fed into the main pipe through the pipeline connected downstream from the reduction in cross-section, in which the pressure is lower. In that device, a certain pressure difference must be produced in the main line so that the force of the spring against the diaphragm piston of the pump can be overcome and enable the pump to work. Accurate metering, as is necessary for plant-protecting compositions, cannot be achieved with that device. The adjustment of the concentration of fertilizer in the water flow has to be undertaken by modifying the pressure difference in the main pipe. The concentration cannot be adjusted accurately in this way.
Finally, DE-U-88 09 599 discloses a spraying device in the form of a hand-held spray pipe, there being mounted at the outlet end of the spray pipe a one-way supplementary fluid dispenser consisting of a cylindrical housing and a piston displaceably arranged therein on a guide tube. Primary fluid from the spray pipe flows out through this guide tube into an outlet nozzle on the supplementary fluid dispenser, whilst a partial flow of the primary fluid acts on the piston, so that the supplementary fluid contained in the supplementary fluid dispenser is forced by means of the piston into the outlet nozzle in which it is mixed with the primary fluid emerging from the guide tube. Exact metering is not possible with this device because it is not possible for the piston in the supplementary fluid dispenser to be moved from its rest position by a small amount of primary fluid. Also, because of the friction of the piston in the housing, metering cannot be predetermined and adjustment of the concentration of supplementary fluid in the primary fluid is not possible.